1. Field of Invention
The invention relates to a power control device and a method thereof and, in particular, to a power control device and a method thereof of multi base powers for an optical disk drive.
2. Related Art
An optical read/write module of an optical disk drive is easily affected by heat thus the performance and accurate of the electric device may be influenced. In order to control the electric device at different temperatures, a proper control module must be designed to modify the affection resulted from the thermal factor.
Referring to FIG. 1, an optical disk drive 1 includes an optical pickup module 11 and a power control module 12. The optical pickup module 11 includes a light-emitting unit 111, a light-sensing module 112, and a plurality of current control units 113, 114, 115 and 116. The light-sensing module 112 detects the output power of the light-emitting module 111 and generates a power feedback signal 112A. The power control module 12 determines whether the output power of the light-emitting unit 111 reaches a target value according to the power feedback signal 112A, and generates a power control signal 121 according to the determination. In addition, the current control units 113 to 116 modulate the currents 113A to 116A according to the power control signal 121, respectively. Therefore, after being driven by the currents 113A to 116A, the light-emitting unit 111 generates the output power reaching the target value.
Referring to FIG. 2, when the light-emitting unit 111 is at a temperature T1, the output power and the operating current of the light-emitting unit 111 are related in a line L1. In other words, when the operating temperature of the light-emitting unit 111 is at the temperature T1 and the operating current is at currents Ic, Ib, Iw, or Is, the light-emitting unit 111 generates the output power at powers Pb, Pe or Pw.
In order to control the operating currents generated by the light-emitting unit 111 exactly at the different powers, the conventional power control module 112 controls the currents 113A, 114A, 115A and 116A respectively to be equal to the current Ic, the current Ib minus the current Ic, the current Iw minus the current Ib, and the current Is minus the current Iw. Besides, the light-emitting unit 111 can be driven by the different combinations of the currents 113A to 116A.
For example, if the power control module 12 controls the light-emitting unit 111 to generate the output power at the power Pb, the current control units 113 and 114 are enabled by the power control module 12. Therefore, the light-emitting unit 111 is driven only by the currents 114A (current Ic) and 115A (current Ib minus current Ic) to generate the output power at the power Pb.
On the other hand, if the temperature of the light-emitting unit 111 rises to a temperature T2, the power control module 12 increases the operating current of the light-emitting unit 111 (as dotted line A) with a closed feedback control method based on the power Pw according to the power feedback signal 112A until the output power of the light-emitting unit 111 reaches the power Pw. Besides, for accurately controlling the output power of the light-emitting unit 111 at temperature T2, the power control module 12 increases the operating current of the light-emitting unit 111 (as dotted line A) with a closed feedback control method based on the power Pb until the output power of the light-emitting unit 111 reaches the power Pb. Herein, the output power of the light-emitting unit 111 is controlled by a double-base power controlling method.
Take the power Pw as the base power for an example, the operating current of the light-emitting unit 111 is still equal to the current Iw, such that the light-emitting unit 111 generates the output power at the power Pw′. In order to adjust the output power of the light-emitting unit 111 to the power Ps, the power control module 12 computes the current Is′ resulting in the power Ps according to the current Iw and the relationship between the power Pw and the power Ps, as shown in formula 1.
                              I          w          ′                =                                                            P                w                                            P                c                                      ⁢                          (                                                I                  c                  ′                                -                                  I                  c                                            )                                +                      I            w                                              (        1        )            
In addition, A current Ic′ and Ib′ resulting in the power Pc and Pb is computed in the same computing method. Therefore, the power control module 12 can control the currents 113A, 114A, 115A and 116A respectively be equal to the current Ic′, the current Ib′ minus the Ic′, the current Iw minus the Ib and the current Is′ minus the Iw′. Accordingly, the light-emitting unit 111 is able to generate the output power at different powers (Pc, Pb, Pw and Ps) at the temperature T2. In brief, the conventional technology is to compute the operating-currents of the light-emitting unit 111 to generate the output power at different powers at the temperature T2 according to the line L2.
However, when the light-emitting unit 111 actually reaches the temperature T2, the output power and the operating current of the light-emitting unit 111 are not related in the line L2 but a line L3. Therefore, the operating current computed according to the conventional technology is the current Is′, so that the light-emitting unit 111 generates the output power at power Ps′ (as dotted line B), which is not correctly controlled at power Ps. In the same manner, the light-emitting unit 111 does not generate the output power at power Pc correctly. More particularly, the power Pw and Pb of the light-emitting unit 111 can be accurately controlled by the above-mentioned feedback method. The errors in the above cases are caused by that the conventional technology ignores the threshold-current It and It′ (intersection points of line L1 and line L3 with the current axis, respectively). As shown in FIG. 3, the temperature of the light-emitting unit 111 is in exponential relation to the threshold-current. If the threshold-current is insufficient, the operating-current computed by the conventional technology for obtaining the output power at different temperature would not have an obvious error. However, if the threshold-current is sufficient or the output power is to be precisely controlled, the error of the operating-current computed by the conventional technology is inevitable.
Referring to FIG. 4, the light-emitting unit 111 of the conventional optical pickup module 11 generates the output power Pout to access an optical disk by a repeat writing controlling way. If the temperature of the light-emitting unit 111 changes (for example, increasing the temperature), the output power Pout is well controlled at the writing power Pw and bias power Pb but not the writing power Pw and cooling power Pc due to the regardless of the threshold-current. Further, according to the increase of the temperature, the output power Pout lapses from the writing power Pw and cooling Pc (the dotted line in FIG. 4). And, the optical pickup module 11 can not access the optical disk. Therefore, the optical pickup module 11 does not correctly access the optical disk, and, even more, the lifetime of the optical pickup module 11 and the endurance of the optical disk drive 1 are reduced.
It is therefore a subject of the invention to provide an optical disk drive with multi-power-baseline control, which considers an effect of the threshold current of the optical read/write module in the optical disk drive at different temperature, and computes the operating current for driving the optical read/write module to generate the distinct output power according to a single power-baseline. Thus, the output power of the optical read/write module can be precisely controlled.